1. Field of the Invention
The invention herein relates to liquid filtration devices. More particularly it relates to those types of liquid filtration devices known as xe2x80x9csanitary elementsxe2x80x9d or xe2x80x9csanitary style elementsxe2x80x9d.
2. Description of the Prior Art
In the filtration of many liquids, such as beverage liquids, foods and pharmaceuticals, high purity of the product is required. Therefore it is necessary to clean the filtration system and media frequently. In such filtration equipment, it is intended for the cleaning liquid to have good access to all surface areas of the filtration membrane, so that bacterial concentrations or other contaminants will not accumulate or persist and any material which may contribute to the accumulation or growth of such contaminants or bacteria can be removed.
In the past, however, the designs of sanitary elements have been such that pockets of contaminants, bacteria, bacterial growth materials and the like can form and persist, notwithstanding the periodic washings.
Some prior art filters have incorporated various types of seals at various locations in the filter element, with the intention of trying to insure that contaminants are kept out, but such seals have had scant success. Moreover they have added complexity to the filter element structure, and in doing so have caused other problems such as reducing filter capacity by taking up internal space (the external dimensions of filter elements normally being fixed by the dimensions of the housings into which the filters are to be placed) or leading to increases in filter failures.
Another problem in prior art filters has been unwanted adhesion of the membranes to the feed spacer elements of the leaves. Designs and manufacturing methods have made it possible for contact adhesions to occur other than where the adhesive is supposed to be placed. Such adhesions not only reduce the efficiency of the filter during operation, but also contribute to the formation of inaccessible pockets of contamination.
The solid apertured bypass framework (xe2x80x9ccagexe2x80x9d) around the sanitary element membrane filtration assembly has usually been designed for maximum openness, which has reduced stiffness and allowed for breakage and distortion of the ribs of the cage. Better design could provide both optimum openness and strength.
Finally, indicia on the filters, such as serial numbers, model numbers, and other nomenclature, have been printed with inks that are commonly washed away over the course of the repeated cleaning cycles. The ability to label filters with permanent indicia would be advantageous.
I have now developed a new sanitary filter element which overcomes these deficiencies of the prior art devices and provides a structure which cannot harbor contaminants, including bacteria, and is readily and thoroughly cleaned as needed. The new device has a hollow fluid-permeable core from which extend, preferably in spiral-wound configuration, a number of leaves. Each leaf is formed of two membrane filter sheets with a tricot sheet for fluid channeling adhered between them. The tricot sheet and both membrane filter sheets all have two sides. Each side of the tricot sheet is in surface contact with a xe2x80x9cdischargexe2x80x9d side of its adjacent membrane filter sheet. The side of the each membrane filter sheet opposite its discharge side is the xe2x80x9cfluid contactxe2x80x9d side. The present invention includes a uniquely configured adhesive barrier component along the edges of the membrane filter and tricot sheet of each leaf. Both fluid contact sides of the membrane filter sheets are exposed to fully turbulent flow during operation of the element. Such configuration eliminates structures within the filter where the liquid is quiescent, and where bacterial and other contamination, or materials which support such contaminants, can accumulate. In addition, a novel cage structure provides good fluid flow while having improved strength.
In the manufacture of the element of the present invention, the adhesive is applied as a bead near the peripheral edge or edges of the tricot sheet or the discharge sides of the membrane filter sheets, except at that edge of the tricot sheet which is attached to or faces in the direction of the central core of the element. Once the membrane filter sheets and the tricot sheet have been brought into contact, the adhesive is forced through the tricot sheet, thus adhering the tricot sheet to the two membrane filter sheets, while forming a fluid-tight barrier (usually U-shaped) barrier defining most of the tricot sheet as a fluid-collection pocket. Forcing the adhesive through the tricot sheet also spreads out the adhesive and causes formation of rounded stretches of the adhesive barrier at each point where there is a significant change in the direction of the edge of the tricot sheet, such as at a corner of the tricot sheet. This eliminates the inclusion of small volumes within the tricot sheet where contaminants could collect.
It is preferred to have a feed spacer present between each pair of adjacent leaves, in contact with the exterior fluid contact sides of the leaves. The feed spacers facilitate the flow of the incoming contaminated fluid and help maintain the turbulent flow regime within the element. During manufacture a temporary separation sheet is positioned between each fluid contact side of each membrane and the feed spacer, to prevent the occurrence of random unwanted contact adhesions between the two before and during the curing of the adhesive which bonds the membrane filter sheets.
Therefore, in a broad embodiment, the invention involves a sanitary filter comprising a central fluid permeable core having extending therefrom a plurality of leaves, each leaf comprising a pair of membrane filter sheets having adhered therebetween a tricot sheet, each membrane filter sheet, when in contact with a fluid containing a first concentration of ionic or particulate materials, separating the fluid into a first portion containing a lesser concentration of the materials and a second portion containing a greater concentration of the materials, for discharging the first portion to the tricot sheet and for discharging the second portion other than to the tricot sheet; the tricot sheet for channeling flow of the first portion to and into the fluid permeable core, with the tricot sheet having a peripheral edge; an adhesive for adhering each pair of the membrane filter sheets to the tricot fluid channeling sheet therebetween, and being disposed through the tricot fluid channeling sheet to form a fluid-tight barrier along the peripheral edge of the tricot fluid channeling sheet except for a portion of the edge adjacent the core, the barrier being free of areas wherein quiescent pools of the fluid containing contaminants may form; a cage surrounding at least a portion of the core and leaves; and a housing surrounding the cage and leaves and restraining the core and leaves.
Specific embodiments and preferred aspects of the invention will be described below.